/* mm.c
 *
 * NOTE TO STUDENTS: Replace this header comment with your own header
 * comment that gives a high level description of your solution.
 */
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "mm.h"
#include "memlib.h"

/* If you want debugging output, use the following macro. When you hand
 * in, remove the #define DEBUG line. */
#define DEBUG
#ifdef DEBUG
# define dbg_printf(...) printf(__VA_ARGS__)
#else
# define dbg_printf(...)
#endif

/* do not change the following! */
#ifdef DRIVER
/* create aliases for driver tests */
#define malloc mm_malloc
#define free mm_free
#define realloc mm_realloc
#define calloc mm_calloc
#endif /* def DRIVER */

#define WSIZE       4       /* Word and header/footer size (bytes) */ 
#define DSIZE       8       /* Double word size (bytes) */
#define CHUNKSIZE  (1<<12)  /* Extend heap by this amount (bytes) */
#define MAX(x, y) ((x) > (y) ? (x) : (y))

#define PACK(size, alloc)  ((size) | (alloc)) 
#define GET(p)       (*(unsigned int *)(p))
#define PUT(p, val)  (*(unsigned int *)(p) = (val))
#define GET_SIZE(p)  (GET(p) & ~0x7)
#define GET_ALLOC(p) (GET(p) & 0x1)

#define HDRP(bp)       ((char *)(bp) - WSIZE)
#define FTRP(bp)       ((char *)(bp) + GET_SIZE(HDRP(bp)) - DSIZE) 
#define NEXT_BLKP(bp)  ((char *)(bp) + GET_SIZE(((char *)(bp) - WSIZE))) 
#define PREV_BLKP(bp)  ((char *)(bp) - GET_SIZE(((char *)(bp) - DSIZE))) 

/* Global variables */
static char *heap_listp = 0;  /* Pointer to first block */  

/* single word (4) or double word (8) alignment */
#define ALIGNMENT 8
#define ALIGN(p) (((size_t)(p) + (ALIGNMENT-1)) & ~0x7)

int mm_init(void);
static void *extend_heap(size_t words);
static void place(void *bp, size_t asize);
static void *find_fit(size_t asize);
static void *coalesce(void *bp);
void *malloc(size_t size);
void free(void *bp);
void *realloc(void *ptr, size_t size);
void *calloc(size_t nmemb, size_t size);

/* Initialize: return -1 on error, 0 on success. */
int mm_init(void) {
    if ((heap_listp = mem_sbrk(4*WSIZE)) == (void *)-1) 
        return -1;
    PUT(heap_listp, 0);                          /* Alignment padding */
    PUT(heap_listp + 1*WSIZE, PACK(DSIZE, 1));   /* Prologue header */ 
    PUT(heap_listp + 2*WSIZE, PACK(DSIZE, 1));   /* Prologue footer */ 
    PUT(heap_listp + 3*WSIZE, PACK(0, 1));       /* Epilogue header */
    heap_listp += 2*WSIZE;

    /* Extend the empty heap with a free block of CHUNKSIZE bytes */
    if (extend_heap(CHUNKSIZE/WSIZE) == NULL) 
        return -1;
    return 0;
}

/* extend_heap - Extend heap with free block and return its block pointer */
static void *extend_heap(size_t words) {
    char *bp;
    size_t size;

    /* Allocate an even number of words to maintain alignment */
    size = (words % 2) ? (words + 1) * WSIZE : words * WSIZE; 
    if ((long)(bp = mem_sbrk(size)) == -1)      // return NULL if mem_sbrk reaches maxlimit or input minus number
		return NULL;

    /* Initialize free block header/footer and the epilogue header */
    PUT(HDRP(bp), PACK(size, 0));         /* Free block header */   
    PUT(FTRP(bp), PACK(size, 0));         /* Free block footer */   
    PUT(HDRP(NEXT_BLKP(bp)), PACK(0, 1)); /* New epilogue header */ 

    /* Coalesce if the previous block was free */
    return coalesce(bp);
}

/* malloc */
void *malloc(size_t size) {
    size_t asize;      /* Adjusted block size */
    size_t extendsize; /* Amount to extend heap if no fit */
    char *bp;      

    if (heap_listp == 0)
        mm_init();
    /* Ignore spurious requests */
    if (size == 0)
        return NULL;

    /* Adjust block size to include overhead and alignment reqs. */
    if (size <= DSIZE)
        asize = 2*DSIZE;
    else
        asize = DSIZE * ((size + (DSIZE) + (DSIZE-1)) / DSIZE); 

    /* Search the free list for a fit */
    if ((bp = find_fit(asize)) != NULL) {
        place(bp, asize);
        return bp;
    }

    /* No fit found. Get more memory then place the block */
    extendsize = MAX(asize,CHUNKSIZE);                 
    if ((bp = extend_heap(extendsize/WSIZE)) == NULL)  
        return NULL;                                  
    place(bp, asize);
    return bp;
} 

/* place - Place block of [asize] bytes at start of free block bp 
 *         and split if remainder would be at least minimum block size
 */
static void place(void *bp, size_t asize) {
    size_t csize = GET_SIZE(HDRP(bp));  // csize - original size of this free block

    if ((csize - asize) >= (2*DSIZE)) { // left more than 4 words empty
        PUT(HDRP(bp), PACK(asize, 1));  // Set head of new block
        PUT(FTRP(bp), PACK(asize, 1));	// Set foot of new block
        bp = NEXT_BLKP(bp);
        PUT(HDRP(bp), PACK(csize-asize, 0));  // Set head of left free block
        PUT(FTRP(bp), PACK(csize-asize, 0));  // Set foot of left free block
    }
    else {								// left less than 2 free words - all include in new block
        PUT(HDRP(bp), PACK(csize, 1));
        PUT(FTRP(bp), PACK(csize, 1));
    }
}

/* find_fit - Find a fit for a block with asize bytes */
static void *find_fit(size_t asize) {
    /* First-fit search */
    void *bp;
    for (bp = heap_listp; GET_SIZE(HDRP(bp)) > 0; bp = NEXT_BLKP(bp))
        if (!GET_ALLOC(HDRP(bp)) && (asize <= GET_SIZE(HDRP(bp))))   // If (!alloced && large enough)
            return bp;
    return NULL; /* No fit */
}

/* free - Free a block */
void free(void *bp) {
    if (bp == NULL) 
        return;

    size_t size = GET_SIZE(HDRP(bp));
    if (heap_listp == 0)
        mm_init();

    PUT(HDRP(bp), PACK(size, 0));
    PUT(FTRP(bp), PACK(size, 0));
    coalesce(bp);   // coalesce if previous or next block is free
}

/* coalesce - Boundary tag coalescing. Return ptr to coalesced block */
static void *coalesce(void *bp) {
    size_t prev_alloc = GET_ALLOC(FTRP(PREV_BLKP(bp)));
    size_t next_alloc = GET_ALLOC(HDRP(NEXT_BLKP(bp)));
    size_t size = GET_SIZE(HDRP(bp));

    if (prev_alloc && next_alloc)              /* Case 1 - both alloced */
        return bp;

    else if (prev_alloc && !next_alloc) {      /* Case 2 - coalesce only next block */
        size += GET_SIZE(HDRP(NEXT_BLKP(bp)));
        PUT(HDRP(bp), PACK(size, 0));
        PUT(FTRP(bp), PACK(size, 0));
    }

    else if (!prev_alloc && next_alloc) {      /* Case 3 - coalesce only previous block */
        size += GET_SIZE(HDRP(PREV_BLKP(bp)));
        PUT(FTRP(bp), PACK(size, 0));
        PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
        bp = PREV_BLKP(bp);
    }

    else {                                     /* Case 4 - coalesce all three blocks */
        size += GET_SIZE(HDRP(PREV_BLKP(bp))) + GET_SIZE(FTRP(NEXT_BLKP(bp)));
        PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
        PUT(FTRP(NEXT_BLKP(bp)), PACK(size, 0));
        bp = PREV_BLKP(bp);
    }
    return bp;
}

/* realloc - you may want to look at mm-naive.c */
void *realloc(void *ptr, size_t size) {
    size_t oldsize;
    void *newptr;

    /* If size == 0 then this is just free, and we return NULL. */
    if(size == 0) {
        mm_free(ptr);
        return 0;
    }

    /* If oldptr is NULL, then this is just malloc. */
    if(ptr == NULL)
        return mm_malloc(size);

    newptr = mm_malloc(size);

    /* If realloc() fails the original block is left untouched  */
    if(newptr == NULL)
        return 0;

    /* Copy the old data. */
    oldsize = GET_SIZE(HDRP(ptr));
    if(size < oldsize) 
    	oldsize = size;
    memcpy(newptr, ptr, oldsize);

    /* Free the old block. */
    mm_free(ptr);

    return newptr;
}


/* calloc - look at mm-naive.c
 * This function is not tested by mdriver, but it is
 * needed to run the traces.
 */
void *calloc (size_t nmemb, size_t size) {
    size_t bytes = nmemb*size;
    void *newptr;

    newptr = mm_malloc(bytes);
    memset(newptr, 0, bytes);
    return newptr;
}

/* Return whether the pointer is in the heap.
 * May be useful for debugging.
 */
static int in_heap(const void *p) {
    return p <= mem_heap_hi() && p >= mem_heap_lo();
}

/* Return whether the pointer is aligned. 
 * May be useful for debugging.
 */
static int aligned(const void *p) {
    return (size_t)ALIGN(p) == (size_t)p;
}

/* mm_checkheap */
void mm_checkheap(int lineno) {
}
